"Ustilago maydis is a dimorphic corn pathogenic basidiomycota. U. maydis haploid cells are able to grow in liquid synthetic where at pH 7 grows as yeast, while at pH 3 it develops in the mycelial form. Two-dimensional gel electrophoresis coupled with LC ESI/MS-MS was used to analyze the differential accumulation of proteins in the yeast and the mycelial morphologies. 2-DE maps were obtained in the pH range of 5-8 where 404 total protein spots were separated, from these 43 were differentially accumulated when comparing strains (FB2wt and constitutive yeast or mycelial mutants, CL211 and GP25, respectively) growing at pH 7 against pH 3. Topoisomerase2, thioredoxin, and Vdac were up-accumulated in mycelial form while Hpm1 DNA binding protein and aldo keto reductase were downaccumulated. The down-accumulation in CL211 of several transcription factors such as Btf3a, could be related with the MAPK pathway, while mutation in gcn5 (GP25) was reflected in the down-accumulation of Mge1 and Lpd1- dihydrolipoamide dehydrogenase. Lys12 was up-accumulated in the mycelial form in both FB2wt and GP25 at pH 3. This protein has been reported as a new target for antifungal drugs. Specific proteins related to dimorphism were found whenproteins affected by changes in the medium pH were eliminated; then dimorphism was related with the up-accumulation of CipC and down-accumulation of Hmp1.Our results complement the information about the genes and proteins related with the dimorphic transition in U. maydis."